Induction PP Questions, Standards, NPO, and Stages
Denitrogenation
Purpose: remove Nitrogen (78% of RA) from the FRC, replacing it with O2, to increase safe apneic time from 1-2 minutes to 8-10 minutes. This gives you more time to secure an airway.
Because obese and pregnant patients inherently have a smaller FRC, they have a much shorter safe apneic period, even with proper denitrogenation. Some strategies may be proclive (25 degree tilt), ramping (pillows underneath neck/shoulders), or apneic oxygenation (e.g., HFNC).
Doing denitrogenation for longer than needed will not give more apneic time because there is only so much time your FRC can hold onto it
The best way is to do ACTIVE denitrogenation; do not just passively place the mask on the patient (even straps). This ensures you are actually getting 100% FiO2 to the patient instead of having room air entrainment (leaking of RA into the mask space d/t Bernoulli’s law). Even providing >5L (usually 10L) O2 will provide 100% this way, as the usual 15L for 100% FiO2 in ICU was d/t face masks/NC versions of oxygen delivery
In-depth explanation: When oxygen flows through a tube that narrows (a constriction or "venturi"), the gas molecules must speed up to get through the narrow gap. As they accelerate, their kinetic energy increases. To conserve energy, their potential energy (lateral pressure against the walls of the tube) must drop. Key takeaway: High speed = Low pressure.
If you place a hole (an "entrainment port", such as from a poor mask seal) at that exact low-pressure spot, the higher-pressure room air is "sucked" into the stream of oxygen. This is entrainment.
If at this point, you are unable to provide adequate ventilation, you can:
Reposition airway/patient
Insert OPA
LMA
Related gas laws:
Dalton’s Law of Partial Pressures: This is the primary law that states that the total pressure is the sum of the partial pressures of all gases in the mixture. The room air (nitrogen) entering the leak adds its own partial pressure to the mix, which mathematically must decrease the partial pressure of oxygen to keep the total pressure at 1 atm (760 mmHg).
The Math: At sea level 760 mmHg, you shift the inhaled gas from PO2 160 mmHg to PO2 760 mmHg. By increasing the fractional concentration of oxygen, Dalton’s Law dictates that the partial pressure of oxygen must rise, displacing nitrogen.
Fick’s Law of Diffusion: As the concentration gradient of oxygen increases in the alveoli, it drives the diffusion of oxygen across the alveolar-capillary membrane into the blood.
Pressure Gradient: By filling the alveoli with 100% O2, you create a massive pressure gradient between the alveoli and the pulmonary capillary blood. According to Fick’s Law, the rate of diffusion is directly proportional to this pressure gradient, thus forcing oxygen into the blood rapidly while nitrogen follows its own gradient out of the blood and into the alveoli to be exhaled.
What are the three critical endpoints to complete denitrogenation properly?
100% fio2 at normal tidal volume breathing for 3 min
3-8 forced vital capacity breaths (max in and max out)
Gold standard: End-tital O2 >85%
Confirming Ability to Ventilate
This is only done in a typical induction sequence; it is done after administering the induction agent and before the NMBDs
Purpose: last “out” in case you are unable to ventilate when they are already paralyzed.
The argument against this step is a false sense of security; just because you can ventilate before paralysis, does not necessarily mean you can ventilate after paralysis or vice-versa. Thus, this step does not preclude (aka, stop) the use of inducing muscle relaxation. In fact, a muscle relaxer may make it easier to ventilate them.
Intubation
While muscle relaxation is the "gold standard" because it provides the best view and prevents the patient from coughing or bucking (which can cause vocal cord trauma), it is not a requirement for intubation
You can also perform inhaled induction, awake fiberoptic intubation, or LMA without NMBDs
ASA Difficult Airway Algorithm:
1) Anticipated Difficult Airway: If you suspect difficulty during your pre-op assessment, the primary goal is safety through preservation of spontaneous ventilation.
Primary Choice: Awake Intubation via fiberoptic
Alternative: If awake intubation is not feasible or fails, consider regional anesthesia (if appropriate for the surgery) or cancelling the case to optimize the patient.
2) Unanticipated Difficult Airway (The "Entry" into the Algorithm)
THE FIRST STEP IS TO CALL FOR HELP
Step A) Failure of Intubation: Optimize by ensuring proper positioning (sniffing position), use a bougie, change blade size/type (e.g., switching to video laryngoscopy), and ensure adequate paralysis.
Tips: Try UP TO 3 times, but no more. +1 if better qualified expert arrives
Step B) "Can You Ventilate?" Decision Point:
If Ventilation is Adequate: You have time. You may switch to a LMA as a conduit or rescue, or wake the patient up.
If Ventilation is Inadequate: You are entering the "Emergency Pathway."
Step C) The Emergency Pathway (Cannot Intubate and Cannot Ventilate):
Try a second-generation LMA
One last attempt at mask ventilation or intubation using an alternative device.
Emergency Invasive Airway via Crike
ETT Characteristics
Typical sizing is 7.0-7.5 for females or 8.0-8.5 for males
Can also be determined by lean body mass (e.g., children), type of surgery (e.g., microlaryngeal with small ETT vs thoracic surgery with double lumen tube), edema
Children (uncuffed): Age / 4 + 4
Cuffed will be -0.5 ETT internal diameter
Remember Psouille’s Law; While a smaller tube is easier to pass, a larger tube significantly decreases the work of breathing and allows for easier suctioning of secretions and better fiberoptic access (e.g., bronchoscopy).
Tip: While the Poiseuille formula focuses on general flow rate, the Reynolds equation is what you use to determine the transition to turbulence. Thus, you can not just flip/invert the equations around.
Typical insertion depth is 21 cm for females or 23 cm for males (3-5 cm above the carina to give the ETT some wiggle room on patient position changes)
Add +4 cm if inserting through nose
Cuff pressure should theoretically be monitored with manometry to maintain <20 cm H2O. However, pilot balloon palpation is simply used most of the time to get a “rough estimate”
Remember that N2O can further increase the cuff size and should be frequently checked/burped throughout the case
The best way to verify ETT placement is capnography; the second best verification method is direct visualization of the ETT going through the cords
BONUS: The reservoir bag size should be patient’s weight in kg x 3
Ventilator
Open APL (0) = spontaneous breathing
Closed APL (up to 70, but typically maintain <20 cm H2O until secured airway achieved, by which point increasing past this pressure is not inherently dangerous in relation to gastric insufflation, although barotrauma can definitely still occur) = positive pressure
Ideal settings:
6-8 ml/kg Vt (ideal body weight; remember that lungs don’t change much in volume even when someone is obese)
You should also go on the lower end of Vt if someone has low compliance or is having one lung ventilation
RR 10-16 (increase if you want to blow off CO2, like when CO2 gastric insufflation is done or in a ICP state)
I:E 1:2
Fio2 to equal > 94% Spo2
Goal is to achieve MV 5-8 L/min, peak pressures <30 cm H20
PaCO2 to EtCO2 gradient should be 5 to 10 mmHg (under general anesthesia; normal is 2-5). Remember that this gradient exists because of alveolar dead space, which dilutes the exhaled CO2 and makes EtCO2 slightly lower than the actual arterial blood level
EX: If your EtCO2 is 25, your PaCO2 is likely 30–35. If your EtCO2 is 35, your PaCO2 is likely 40–45 (which is perfect physiological normal). BUT If you see 25, you should be asking yourself, "Am I over-ventilating this patient, or is there a surgical reason (like a craniotomy) why I want them this low?"
Drug Info
Is administration of inhaled anesthetic agent prudent during the step of providing adequate ventilation? Additional dosing of induction agents?
Administration is generally not prudent. Even though it bridges the gap between the induction/muscle relaxant and DL, you would only have it turned on for a small amount of time that would not be useful basically, but it also can’t hurt.
What if a lesser dose of muscle relaxant was used due to an anticipated short surgical procedure time?
Giving a "half-dose" of an NDMR to save time at the end of the case prolongs the onset time significantly. You may find yourself mask-ventilating for 5+ minutes waiting for intubating conditions that never fully materialize. It is often better to give a full intubating dose of Rocuronium for the best view and then reverse it with Sugammadex at the end, rather than struggling with poor conditions during a "light" block.
When might it be appropriate to provide less than 1 MAC of volatile agent?
The most frequent reason to use less than 1 MAC is when you are utilizing a balanced technique. By combining multiple classes of drugs, you achieve the same depth of anesthesia while minimizing the side effects of any single agent. EX: Synergy with Opioids, Adjuncts (e.g., propofol infusions, ketamine, dexmedetomidine, or nitrous oxide, regional anesthesia)
Neuro monitoring: SSEP or MEPs (evoked potential monitoring) need reliable monitoring without distortion caused by volatile anesthetics
Acute alcohol use, CNS depressants, hypothermia, hyponatremia, hypoxia, metabolic acidosis, CABG, hypotension
What is the literature for defasciculating doses to prevent postop myalgia d/t succ?
Postop myalgia is more common in less-muscled individuals like Females. De-fasciculation (small doses of a non-depolarizer) has strong evidence to support it reducing postop myalgia.
Process: 5-10 mg of Roc (BEFORE THE INDUCTION medications to partially block some of the receptors before proceeding to give sux). This is roughly 1/10 of ED95, so 0.03 mg/kg of Roc, which would cause faster onset of the muscle relaxer in and of itself
Process: During denitrogenation, give defasculating dose, monitoring for difficulties to swallow or after 2 minutes. Give your propofol, monitor for loss of lid reflex. Give your sux.
Can cause distress in the patient d/t muscle weakness and SOB d/t difficulty breathing, so work quickly
Should you give fentanyl in every patient induction?
No, because then you deal with hypotension as there is such a long wait while the room is prepping, plus you gave propofol. More applicable for longer DLs (by inexperienced providers) rather than a fast DL (by experienced providers)
Fentanyl will be more commonly used for lower ASA and younger patients (synergistic effect with Versed), but even then you make sure to not turn on the full MAC to decrease chances of hypotension.
Esmolol becoming more popular in last 5 years because of fast on/off DUE TO NON-SPECIFIC ESTERASES.
Additional notes
TOF is more critical for emergence vs induction (which can just use the standard onset time)
Remember that drugs are in RANGES; with a very old patient, go lower on propofol to avoid hypotension and apneic period; just be more patient while waiting for it to work.
It is also ok to give PREVENTATIVE (“chasing” dose) Neo if you expect hypotension from propofol, especially because some people it is harder for them to come back from a drop or cannot even tolerate a slight drop to aortic stenosis.
Spinals: Avoid giving to patients with aortic stenosis, as spinals cause hypotension d/t rapid, dense sympathectomy (vasodilation). Additionally, Spinals themselves do not increase risk of bleeding, but if a person is on AC and has not stopped it properly, spinals have the risk of causing a spinal hematoma
Taping eyes is important to protect the patient from risk of corneal abrasion, which can occur when staff leans over the patient frequently (e.g., dangling ID badges, equipment)
Small bowel obstructions can quickly tank their BP
Use hynotherapy: “after surgery, you are going to be comfortable, hungry, and ready to go home”
Differences between Induction Sequences
Typical Induction:
Indications:
elective/schedule/non-emergent cases
NPO guidelines followed
novice clinician
Main sequence difference:
propofol —> NMBDs has a period of “verifying ability to ventilate” between them. During positive pressure ventilation after giving the NMBDs, mask ventilate until the ETT is secured.
Roc used 0.6-1 mg/kg
Positive pressure after the NMBD is given
RSI:
Indications: Aspiration prophylaxis
full stomach (did not follow NPO guidelines or emergency case)
presumed full stomach (severe GERD, hiatal hernia, pregnancy, bowel obstruction, appendicitis, enteral feedings)
delayed gastric emptying (diabetes, GLP drugs)
Critical hypoxemia
severe obesity
Laryngospasm
open globe injury (d/t coughing/reflux causing rapid increase in IOP)
Difficult airway likely?
Main sequence difference:
Cricoid pressure utilized to prevent aspiration
propofol —> NMBDs without a period of “verifying ability to ventilate” between them (you go straight into it, after of course verifying loss of lid reflex)
Sux 1-1.5 mg/kg or Roc 1.2 mg/kg
NO Positive pressure after the NMBD is given; just wait appropriate amount of time and go into DL
PPV is avoided specifically to prevent gastric insufflation. In a patient with a full stomach, this "extra" pressure can overcome the LES, leading to passive regurgitation of acidic contents into the lungs (Mendelson's Syndrome).
from patho: 60% asymptomatic, 20/15% need some sort of support, 5% die. Giving steroids/abx is not warranted until pneumonia is actually confirmed. Lidocaine however, might decrease neutrophil response to inflammation.
LMA:
Indications:
elective/outpatient surgery not requiring NMBDs (aka, there is spont. breathing)
No/low aspiration risk
Emergency situation (can’t ventilate, can’t intubate)
Main sequence difference:
NO NMBDs
NO Positive pressure (<20 cm H2O)
NO DL
Cricoid Pressure
Even though it is dogmatic, cricoid pressure is still useful and should be utilized, particularly with proper training. Remember that it is better to be safe than sorry, and while it could theoretically cause esophageal rupture, aspiration is the leading cause of anesthetic-related deaths and you should do everything to prevent it
Unlike every other cartilaginous structure in the airway, the cricoid is a complete, solid ring. This "Signet Ring" remains rigid even when you apply downward pressure, which then causes esophageal compression directly between the back of the cricoid ring and the front of C6
If you applied this pressure to the thyroid cartilage, it would likely collapse or hinge inward without effectively occluding the esophagus. If applied to tracheal rings, the open "C" would simply flatten, potentially obstructing the airway without closing the esophagus.
Correct use:
Before LOC/awake state (10 Newtons, 1 kg). Roughly the amount of pressure it takes to painfully press your thumb into a table.
After LOC/asleep state, assessed by loss of lid reflex (30 Newtons, 3 kg). As if you were trying to stop a moderate bleed with your fingers
BURP technique: back (straight back into the spine), up, right pressure (the patient’s Right side)
Stabilization: Use the "three-finger" technique—the thumb and middle finger stabilize the sides of the cricoid to prevent it from tilting, while the index finger applies the downward pressure.
It doesn’t matter if you use a 2 finger technique either
Potential complications: increased LES relaxation promoting reflux if occlusion is not perfect; risk of esophageal rupture if active vomiting present
It is not necessary to remove an NGT/OGT before RSI. Cricoid pressure is effective even with a tube in place
What should you do if the patient begins to regurgitate during induction?
Trendelenburg Position or side lying
Suction
Intubate and Inflate ASAP
Suction the ETT: Before giving a breath through the tube, suction down the ETT to remove any contents that may have already slipped past the cords
ASA Standards
Anesthetic Plan should consider the following:
Duration, invasiveness, site, surgical position
Need for paralytics
inpatient vs outpatient; emergent vs planned
Medical/surgical history of patient; patients preferences; patient age/special needs
Surgeon/anesthesia preferences
14 AANA Standards for Nurse Anesthesia Practice:
The Preparation (Standards 1–3): You meet the patient, get consent, and create a plan.
The Action (Standards 4–11): You start the case, watch the monitors, and keep them safe.
Pulse ox, ECG, and BP should be monitored at least every 5 minutes. Capnography and temp can be added PRN.
The Foundation (Standards 12–14): The "legal/professional" wrapper.
Triad of general anesthesia: skeletal muscle relaxation, amnesia/hypnosis, and analgesia
A theoretical fourth arm to add to this would be autonomic stability (maintain within 20% of the patient’s baseline)
Similar airplane industry: takeoff, maintenance, and landing
Fasting Intervals (The "2-4-6-8" Rule)
2 Hours: Clear liquids (water, fruit juice without pulp, carbonated beverages, clear tea, and black coffee, NO alcohol). This reduces gastric volume and increases gastric pH.
Pills with water sips are allowed up to one hour before surgery
4 Hours: Breast milk
6 Hours: Infant formula, non-human milk, and light meals (toast, clear liquids)
8+ Hours: Fried/fatty foods, full meal.
GI Pharmacologic Prophylaxis:
The ASA advises against the routine use of GI stimulants (metoclopramide), gastric acid blockers (H2 antagonists, PPIs), antacids, or anticholinergics in patients with no apparent increased risk for pulmonary aspiration
High-Risk Patients may receive: Antacids (only non-particulate antacids [e.g., sodium citrate, Bicetra] are recommended).
Particulate antacids include Tums, which release particles into the stomach that can cause inflammatory response/Mendelson’s syndrome.
Non-particulate antacids are clear liquids with <5 minute onset.
Guedel’s Anesthesia Stages
This was originally created for inhaled anesthetics, before multi-modal approach was used. Nowadays, with IV induction medications this progression is largely “skipped over” d/t fast onset. Now this would be more visible in emergence, if at any time.
Stage 1: Analgesia/disorientation
Pt becomes sedated but conversational —> LOC.
Breathing is slow and deep
Stage 2: Excitement/Delirium (the dangerous “gray in-between” area)
Disinhibition, uncontrolled movements, loss of eyelash reflex, hypertension, tachycardia.
Airway reflexes are still intact but hypersensitive. Stimulation here (e.g., insertion or removal of an ETT) risks laryngospasm, vomiting, and aspiration. This is where most bad things happen in anesthesia!
Breathing is rapid and irregular
Goal: go lighter or deeper ASAP to skip over this stage
Stage 3: Surgical Anesthesia (target level)
Ceased eye movements and respiratory depression.
Airway manipulation is safe at this time.
breathing is rapid and shallow
Plane 1: Regular breathing, constricted pupils; eyelid/swallow reflexes disappear.
Plane 2: Loss of laryngeal/corneal reflexes. Respiration may pause (intermittent)
Plane 3: "True surgical anesthesia." Complete relaxation of intercostal/abdominal muscles; loss of pupillary light reflex.
Plane 4: Irregular respiration, paradoxical rib cage movement, and full diaphragm paralysis resulting in apnea
Stage 4: Overdose
Medullary depression, cessation of respiration, weak/thready pulse, flaccid muscles, fixed/dilated pupils.
Lethal without CV and resp support.
Interpretation: too much anesthetic was given for the level of surgical stimulation.
Extubation Tips
If you need to reintubate —>
if sux was originally administered, give Roc
if Roc then sugammedex was given, sux is better to give bc more Roc would be instantly removed with the still-circulating sugammedex
Typically, planning for extubation begins about 30 minutes prior to closure; but do not un-paralyze them until sutures are closed for more painful surgeries (e.g., lap chole)
In order to potentiate this, remember that the only true way to get rid of inhaled anesthetic is via ventilation
To encourage the patient to breathe, you can change vent settings to make them acidotic and build up the threshold to breathe on their own (by decreasing the RR). Usually you would transition to PSV mode once the patient starts breathing on their own.